Various types of leadframe designs are currently used in the semiconductor industry for packaging semiconductor die. One such known leadframe is shown in FIG. 1. As illustrated, FIG. 1 depicts a leadframe 10 having a flag 12 and a plurality of leads 14 having inner lead portions that terminate at lead tips 16, the lead tips 16 defining a die receiving area. The flag 12 receives and supports a semiconductor die 50. Each lead 14 includes an exposed lead portion 22 (which is exposed from the packaged semiconductor device), and a bond finger 18 (which is encapsulated by the plastic encapsulant material). Each bond finger 18 includes a lead tip 16 to which bond wires from the semiconductor die 50 are routed. The flag is supported, prior to singulation and encapsulation, by two sets of tie bars 20, extending parallel to the longitudinal axis of the leadframe, and perpendicular to the short axis of the leadframe.
The leadframe depicted in FIG. 1 is considered an improvement upon a conventional leadframe that has a solid flag. The flag 12 shown in FIG. 1 is generally known in the art as a "window flag," named as such for the opening in the central portion of flag 12. This opening has been incorporated into the flag 12 to increase the plastic/die interface and improve adhesion and reduce the so called "popcorning" effect. As is known in the art, popcorning is a problem associated with plastic encapsulated semiconductor devices, in which devices moisture is trapped by the plastic encapsulant. Upon subsequent heating during processing steps (e.g., solder reflow) the package has the tendency to delaminate internally and have an associated "popping" sound. It is noted that the leadframe depicted in FIG. 1 is designed for a two-sided package, wherein exposed lead portions 22 protrude along only two opposing sides of the finished packaged semiconductor device. As such, the leadframe is generally used in connection with relatively low lead count devices.
FIG. 2 depicts another leadframe design, generally known in the art as an "X-flag" leadframe. The same reference numerals are used in FIG. 2 to depict the same components of the leadframe shown in FIG. 1. The tie bars 20 extend from each of the corners of the leadframe, in contrast to the leadframe shown in FIG. 1. Accordingly, the tie bars are not oriented parallel or perpendicular to either axis of the leadframe (they are 45 degrees with respect to each of the axes). This configuration of the tie bars enables the provision of leads at each of the four sides of the leadframe, and hence to each of the four sides of the final, packaged semiconductor device. As shown, the flag 12 of FIG. 2 takes the form of a "mini-flag" to improve the plastic/die interfacial area and address the popcorning problem noted above. The prior art leadframe shown in FIG. 2 provides an important advantage over that shown in FIG. 1. Particularly, the X-flag leadframe permits use of various die sizes by combining use of the mini-flag and the four tie bars extending along the corners of the package.
The present inventors have recognized a need in the art for providing an improved leadframe design for two-sided packages, particularly, one that permits use of a relatively wide range of die sizes while preventing the popcorning problem. In this regard, turning back to the leadframe shown in FIG. 1, the range of die sizes that can be used is quite limited. Particularly, the die cannot be sized such that it is not adequately supported by the flag (in view of the window or opening formed therein). In addition the die has to be large enough to minimize the amount of exposed flag area, to prevent unwanted shorting between the flag 12 and the bond wires electrically connecting the die 50 to the lead tips 16. On the other hand, the die cannot be sized so as to overlap or otherwise intersect the lead tips 16, so that the bond wires may be connected to the leads 14.